Selecting the right generator for your RV is an important choice and could mean the difference between a week-long headache and a carefree vacation.
What Size RV Generator Do I Need
Sometimes, the road takes you to places where you’re all on your own. Whether that is a local Walmart parking lot (a vanishing possibility) or a remote place to park in the wilderness, you want a reliable source of power that will keep your AC running, the drinks cold, and the lights on. The most reliable source of power for recreational vehicles is a generator.
This leads to other considerations: fuel type, portable or onboard, inverter or conventional, and the most often asked question, “what size do we need?”
Fuel is a practical issue, and whether you choose gasoline, diesel, or propane will probably depend on your RV type, which also plays a role when choosing between an onboard or portable unit.
Onboard or Portable RV Generator
Unless you’re driving a motorhome, van, or truck, chances are good that powering your RV requires a portable generator. However, some travel trailers and fifth-wheel RVs have generator prep options. It’s an option you can order. Onboard RV generators are convenient in that they are always ready to go. Start them from a panel inside your RV and you’re ready to go. Generally speaking, they use the same fuel as your RV engine. Trailers and fifth wheels don’t have engines, so propane is usually the best fuel choice.
Portable RV generators have reached a point where they are almost as convenient as onboard models. Once connected, just push a button a remote fob to start or shut off as needed. Dual-fuel models can run on propane or gasoline.
Who wouldn’t want to explore further? Adventuring off the beaten path is rewarding, especially when you’re not worried about where to park or how to power your RV.
Inverter vs Conventional RV Generator
Inverter generators have some definite advantages over conventional models. More important than fuel economy or noise level is power quality. While it is possible to buy conventional generators with good power quality, the less expensive models typically sold in hardware stores and home centers produce less than ideal power. The higher the load, the more the quality declines.
Be sure to look at the specifications for Total Harmonic Distortion or THD. Sensitive electronics and appliances may not work on power from a generator with a THD greater than 6 percent. Good quality conventional portable generators have a THD of 5 percent or less. Inverter generators are even better with less than 3 percent.
The inverter is not new technology, but have gained popularity in recent years thanks to designs that make them very quiet and fuel efficient. On a standard propane tank, some models will run for 20 hours or longer at 25% load and register sound levels as low as 50 dB. That’s quieter than two people having a conversation. Variable speed engines that only run fast enough to accommodate the load make them exceptionally quiet.
Parallel operation allows two inverter generators to operate as one. A parallel cable connects both generators to an outlet or outlets that combine the power of both units as if they were one. Average power use—just run one generator. Need more power? Start the second have up to double the power of a single unit. This type of connection isn’t possible on a conventional portable generator.
Conventional portable generators are louder and use more fuel. Their engines run at a constant 3600 RPM. Expect noise levels from around 70 to 80 dB. Fuel economy varies, but don’t expect a long run time unless you invest in a large, heavy propane tank.
Need to Know
RV Voltage:
While homes have appliances that run on either 120 volts, 240 volts, or a combination of both, most RVs only run on 120 volts.
30 Amp RV:
The shore power inlet receptacle (3 slots to accept a 3-blade plug) on a 30-amp RV is a 120-volt, 30-amp receptacle. The shore power cable has one 120-volt wire, a neutral wire, and a ground wire. Travel Trailer Ready outlets are the TTR-30 design with a maximum capacity of 30 amps at 120 volts.
30 Amps x 120 Volts = 3600 Watts.
50 Amp RV:
The shore power inlet receptacle (4 slots to accept a 4-blade plug) on a 50-amp RV is a 120/240-volt split-phase receptacle (NEMA 14-50R) with two hot legs, a ground, and a neutral. Each hot leg carries up to 50 amps or 6000 watts each, for a total power capacity of 12000 watts.
The 50-amp RV has over three times the power capacity of a 30-amp RV.
50 Amps x 120 volts x 2 = 12000 watts.
Running Watts:
The power required to run continuously. An LED light bulb might require less than 20 watts to run continuously.
Starting Watts:
The power required to start a motor. Starting watts is a momentary surge of power that starts a motor turning. It only lasts a few seconds. In order to start a motor, a generator must have the starting watts capacity to meet the motor’s starting watts requirement.
A rough rule of thumb states that running watts = 3 x running watts.
If a refrigerator needs 500 watts, it takes 1500 watts to start it. It could be more or less. It depends on the appliance and motor, and whether the motor starts under load.
Generator Ratings:
Manufacturers rate their generators for both starting watts and running watts. Make sure you read the specifications before purchasing. Some manufacturers list their generators with the Max Watts and minimize the runnings watts specification.
This is especially true of portable RV inverter generators.
It is also important to note that most portables, whether inverter or conventional, produce less power while running on propane than they do on gasoline. If you intend to run on propane, buy enough power that the starting and running watts on propane is adequate for your purpose.
Power Margin:
Just like a car might be capable of 120 MPH, but you rarely, if ever, drive it that fast, a generator’s power ratings are maximum values. Realistically, you shouldn’t operate a generator at the maximum running watts for hours or days at a time. It’s hard on the generator, and it won’t last as long.
A good power margin is 75 percent rated load. Operate a 3600 running watt generator at 2700 watts and it will last a lot longer than running it constantly at 3600 watts. It’s okay to run at close to maximum for short periods, but not all the time.
The point is, if you calculate a requirement of 2000 running watts, for example, don’t buy a 2000-watt generator. Buy a 2700-3000-watt generator.
RV Generator Size
If the RV has a 30 Amp or 50 Amp Shore Power inlet, any generator that can provide 30 amps or 50 amps with 25 percent margin is going to work. That’s not necessarily the best choice, however. Remember that the generator must also handle the starting watts of any appliance it powers. Where air conditioners are concerned, that can be a hefty load.
For example, look at a 30-amp RV with a water heater, coffeemaker, refrigerator, and air conditioner. Not an unusual combination of appliances. If we stay on the low end, that’s 1000 watts + 600 watts + 400 watts = a 2000-watt base load. Now the air conditioner kicks on with a 3000 starting watts load for a total (momentary) load of 5000 watts.
Can your generator handle that? What other appliance is using power at the same time? A couple of lights, maybe a fan, and charging the laptop.
Most generators under 4000 running watts lack the capacity to start and run an air conditioner on top of this very reasonable base load.
But. What are the actual power requirements of the appliances in your RV? The size is in the details. Make a list of all your appliances and their current or wattage requirements. Don’t forget the ones you can’t see without opening a cabinet, like the water heater, water pump, and anything else.
Where will your next adventure lead you? Photo Credit: Memory Catcher
What Size Generator For 30 Amp RV
The hungriest power user in your home away from home is probably the air conditioner(s). It might have two or three rooftop AC units, depending on the size of the RV.
A 2000-watt base load is a realistic number for many RVs. When the AC isn’t running, the 2000-watt load is well below our maximum load of 3600 watts for a 30-amp RV. Using a 15000 BTU rooftop air conditioner for our example adds 3000 watts during startup and 1500 while running.
A portable generator with a 5000 starting watts rating will get the AC started and keep it running on top of the base load. Looking at the specs for the Onan 4000-watt onboard RV generator is another example. This generator starts and runs a 15000 BTU air conditioner on top of a 2000 watt base load.
And the good news is, the coffee maker doesn’t take long to brew coffee, and the other big appliances don’t run continuously, so even if the generator runs at 90 percent load for a short time, it’s not going to overtax the generator or shorten its life.
If the AC unit is smaller, say 13,500 or 11,000 BTU, recalculate and choose a different model.
What Size Generator for 50 Amp RV
Larger RVs need more power. For this example, assume a single 15000 BTU Rooftop AC. Depending on the base load, the load with the AC unit could be anywhere between 4000 and 6000 watts. It’s a bigger RV with more appliances and a higher base load. A microwave adds 800 to 1000 watts, which is a good start. Other higher loads include a toaster (1000-1400 watts) and a hair dryer (1200-1800 watts). Add 2000 watts to the base load, and a 6000-7000 watt generator covers the load.
Don’t forget that a 50-amp RV electrical system uses two separate 120-volt supply lines, each with a capacity of up to 6000 watts. To power your RV with a generator requires a unit capable of supplying 120 volts on two lines. That usually means a 120/240 volt receptacle on a portable generator OR an onboard generator that produces 120/240 volts single-phase power. Each of the two hot legs is a separate 120-volt supply at up to 50 amps or 6000 watts, for a total of 12000 watts.
What Size Generator for 50 Amp RV with 2 AC Units
Two 15000 BTU air conditioners will gobble up 3000 watts and require 6000 starting watts. Top that with a base load of 3000 watts, and a 6000-watt generator won’t handle the load.
An 8000-watt generator, either onboard or portable, will handle the load without running at maximum power, depending on your base load. Either an onboard or portable generator with a 120/240-volt capacity will power this scenario.
Image Credit Dom Darbyshire
What Size Generator for 50 Amp RV with 3 AC Units
Three 15000 BTU air conditioners require 4500 running watts and 9000 starting watts. Three big air conditioners probably means the RV is a Class A motorhome or coach powered by a diesel engine. It makes sense to power your rig off the grid with an onboard diesel generator capable of producing 12000 watts or more.
Portables are still an option, but the larger the generator, the more it weighs and the harder it is to move. The higher-capacity inverter generators weigh between 360 and 460 pounds. It takes at least two strong people to lift a unit like that on and off the RV.
Because of the weight issue, the 12kW onboard diesel generator is a better choice. It runs off the vehicle’s main fuel tank, and no one has to risk injury moving a large and awkward generator that weighs over 350 pounds.
The Right RV Generator Size
Everyone is different and prefers their own lifestyle. Some people prefer rustic; others want luxury.
Make decisions on what you need and want, and don’t rely on the salesperson to know how you live. It’s not hard to determine what size generator you need. Just add up the power requirements of your major appliances, like the refrigerator, water heater, and air conditioning, that turn themselves on and off as required. Then add in the heavier loads you might use at the same time to find how much power you really need. Add a 25 percent margin for a good idea of how much power you need.
Photo Credit Jill Wellington
